Re: [patch] detect and correct bad features2 superblock field

[Eric Sandeen <sandeen@sandeen.net>]

David Chinner wrote:
> There is a bug in mkfs.xfs that can result in writing the features2
> field in the superblock to the wrong location. This only occurs
> on some architectures, typically those with 32 bit userspace and
> 64 bit kernels.
> 
> This patch detects the defect at mount time, logs a warning
> such as:
> 
> XFS: correcting sb_features alignment problem
> 
> in dmesg and corrects the problem so that everything is OK.
> it also blacklists the bad field in the superblock so it does
> not get used for something else later on.

Looks good to me, thanks for fixing it up properly.

You can add Reviewed-by: or Acked-by: or whatever is appropriate...
Eric Sandeen <sandeen@sandeen.net>

Thanks,
-Eric

> Signed-off-by: Dave Chinner <dgc@sgi.com>
> ---
>  fs/xfs/xfs_mount.c |   34 ++++++++++++++++++++++++++++------
>  fs/xfs/xfs_sb.h    |   37 ++++++++++++++++++++++++++++++++++---
>  2 files changed, 62 insertions(+), 9 deletions(-)
> 
> Index: 2.6.x-xfs-new/fs/xfs/xfs_mount.c
> ===================================================================
> --- 2.6.x-xfs-new.orig/fs/xfs/xfs_mount.c	2007-11-22 10:25:25.590278381 +1100
> +++ 2.6.x-xfs-new/fs/xfs/xfs_mount.c	2007-11-22 10:31:27.891999961 +1100
> @@ -44,7 +44,7 @@
>  #include "xfs_quota.h"
>  #include "xfs_fsops.h"
>  
> -STATIC void	xfs_mount_log_sbunit(xfs_mount_t *, __int64_t);
> +STATIC void	xfs_mount_log_sb(xfs_mount_t *, __int64_t);
>  STATIC int	xfs_uuid_mount(xfs_mount_t *);
>  STATIC void	xfs_uuid_unmount(xfs_mount_t *mp);
>  STATIC void	xfs_unmountfs_wait(xfs_mount_t *);
> @@ -119,6 +119,7 @@ static const struct {
>      { offsetof(xfs_sb_t, sb_logsectsize),0 },
>      { offsetof(xfs_sb_t, sb_logsunit),	 0 },
>      { offsetof(xfs_sb_t, sb_features2),	 0 },
> +    { offsetof(xfs_sb_t, sb_bad_features2), 0 },
>      { sizeof(xfs_sb_t),			 0 }
>  };
>  
> @@ -455,6 +456,7 @@ xfs_sb_from_disk(
>  	to->sb_logsectsize = be16_to_cpu(from->sb_logsectsize);
>  	to->sb_logsunit = be32_to_cpu(from->sb_logsunit);
>  	to->sb_features2 = be32_to_cpu(from->sb_features2);
> +	to->sb_bad_features2 = be32_to_cpu(from->sb_bad_features2);
>  }
>  
>  /*
> @@ -976,6 +978,26 @@ xfs_mountfs(
>  	xfs_mount_common(mp, sbp);
>  
>  	/*
> +	 * Check for a bad features2 field alignment. This happened on
> +	 * some platforms due to xfs_sb_t not being 64bit size aligned
> +	 * when sb_features was added and hence the compiler put it in
> +	 * the wrong place.
> +	 *
> +	 * If we detect a bad field, we or the set bits into the existing
> +	 * features2 field in case it has already been modified and we
> +	 * don't want to lose any features. Zero the bad one and mark
> +	 * the two fields as needing updates once the transaction subsystem
> +	 * is online.
> +	 */
> +	if (xfs_sb_has_bad_features2(sbp)) {
> +		cmn_err(CE_WARN,
> +			"XFS: correcting sb_features alignment problem");
> +		sbp->sb_features2 |= sbp->sb_bad_features2;
> +		sbp->sb_bad_features2 = 0;
> +		update_flags |= XFS_SB_FEATURES2 | XFS_SB_BAD_FEATURES2;
> +	}
> +
> +	/*
>  	 * Check if sb_agblocks is aligned at stripe boundary
>  	 * If sb_agblocks is NOT aligned turn off m_dalign since
>  	 * allocator alignment is within an ag, therefore ag has
> @@ -1165,11 +1187,10 @@ xfs_mountfs(
>  	}
>  
>  	/*
> -	 * If fs is not mounted readonly, then update the superblock
> -	 * unit and width changes.
> +	 * If fs is not mounted readonly, then update the superblock changes.
>  	 */
>  	if (update_flags && !(mp->m_flags & XFS_MOUNT_RDONLY))
> -		xfs_mount_log_sbunit(mp, update_flags);
> +		xfs_mount_log_sb(mp, update_flags);
>  
>  	/*
>  	 * Initialise the XFS quota management subsystem for this mount
> @@ -1884,13 +1905,14 @@ xfs_uuid_unmount(
>   * be altered by the mount options. Only the first superblock is updated.
>   */
>  STATIC void
> -xfs_mount_log_sbunit(
> +xfs_mount_log_sb(
>  	xfs_mount_t	*mp,
>  	__int64_t	fields)
>  {
>  	xfs_trans_t	*tp;
>  
> -	ASSERT(fields & (XFS_SB_UNIT|XFS_SB_WIDTH|XFS_SB_UUID));
> +	ASSERT(fields & (XFS_SB_UNIT | XFS_SB_WIDTH | XFS_SB_UUID |
> +			 XFS_SB_FEATURES2 | XFS_SB_BAD_FEATURES2));
>  
>  	tp = xfs_trans_alloc(mp, XFS_TRANS_SB_UNIT);
>  	if (xfs_trans_reserve(tp, 0, mp->m_sb.sb_sectsize + 128, 0, 0,
> Index: 2.6.x-xfs-new/fs/xfs/xfs_sb.h
> ===================================================================
> --- 2.6.x-xfs-new.orig/fs/xfs/xfs_sb.h	2007-11-22 10:25:25.598277360 +1100
> +++ 2.6.x-xfs-new/fs/xfs/xfs_sb.h	2007-11-22 10:31:27.891999961 +1100
> @@ -89,6 +89,7 @@ struct xfs_mount;
>  
>  /*
>   * Superblock - in core version.  Must match the ondisk version below.
> + * Must be padded to 64 bit alignment.
>   */
>  typedef struct xfs_sb {
>  	__uint32_t	sb_magicnum;	/* magic number == XFS_SB_MAGIC */
> @@ -145,10 +146,21 @@ typedef struct xfs_sb {
>  	__uint16_t	sb_logsectsize;	/* sector size for the log, bytes */
>  	__uint32_t	sb_logsunit;	/* stripe unit size for the log */
>  	__uint32_t	sb_features2;	/* additional feature bits */
> +
> +	/*
> +	 * bad features2 field as a result of failing to pad the sb
> +	 * structure to 64 bits. Some machines will be using this field
> +	 * for features2 bits. Easiest just to mark it bad and not use
> +	 * it for anything else.
> +	 */
> +	__uint32_t	sb_bad_features2;
> +
> +	/* must be padded to 64 bit alignment */
>  } xfs_sb_t;
>  
>  /*
> - * Superblock - on disk version.  Must match the in core version below.
> + * Superblock - on disk version.  Must match the in core version above.
> + * Must be padded to 64 bit alignment.
>   */
>  typedef struct xfs_dsb {
>  	__be32		sb_magicnum;	/* magic number == XFS_SB_MAGIC */
> @@ -205,6 +217,15 @@ typedef struct xfs_dsb {
>  	__be16		sb_logsectsize;	/* sector size for the log, bytes */
>  	__be32		sb_logsunit;	/* stripe unit size for the log */
>  	__be32		sb_features2;	/* additional feature bits */
> +	/*
> +	 * bad features2 field as a result of failing to pad the sb
> +	 * structure to 64 bits. Some machines will be using this field
> +	 * for features2 bits. Easiest just to mark it bad and not use
> +	 * it for anything else.
> +	 */
> +	__be32	sb_bad_features2;
> +
> +	/* must be padded to 64 bit alignment */
>  } xfs_dsb_t;
>  
>  /*
> @@ -223,7 +244,7 @@ typedef enum {
>  	XFS_SBS_GQUOTINO, XFS_SBS_QFLAGS, XFS_SBS_FLAGS, XFS_SBS_SHARED_VN,
>  	XFS_SBS_INOALIGNMT, XFS_SBS_UNIT, XFS_SBS_WIDTH, XFS_SBS_DIRBLKLOG,
>  	XFS_SBS_LOGSECTLOG, XFS_SBS_LOGSECTSIZE, XFS_SBS_LOGSUNIT,
> -	XFS_SBS_FEATURES2,
> +	XFS_SBS_FEATURES2, XFS_SBS_BAD_FEATURES2,
>  	XFS_SBS_FIELDCOUNT
>  } xfs_sb_field_t;
>  
> @@ -248,13 +269,15 @@ typedef enum {
>  #define XFS_SB_IFREE		XFS_SB_MVAL(IFREE)
>  #define XFS_SB_FDBLOCKS		XFS_SB_MVAL(FDBLOCKS)
>  #define XFS_SB_FEATURES2	XFS_SB_MVAL(FEATURES2)
> +#define XFS_SB_BAD_FEATURES2	XFS_SB_MVAL(BAD_FEATURES2)
>  #define	XFS_SB_NUM_BITS		((int)XFS_SBS_FIELDCOUNT)
>  #define	XFS_SB_ALL_BITS		((1LL << XFS_SB_NUM_BITS) - 1)
>  #define	XFS_SB_MOD_BITS		\
>  	(XFS_SB_UUID | XFS_SB_ROOTINO | XFS_SB_RBMINO | XFS_SB_RSUMINO | \
>  	 XFS_SB_VERSIONNUM | XFS_SB_UQUOTINO | XFS_SB_GQUOTINO | \
>  	 XFS_SB_QFLAGS | XFS_SB_SHARED_VN | XFS_SB_UNIT | XFS_SB_WIDTH | \
> -	 XFS_SB_ICOUNT | XFS_SB_IFREE | XFS_SB_FDBLOCKS | XFS_SB_FEATURES2)
> +	 XFS_SB_ICOUNT | XFS_SB_IFREE | XFS_SB_FDBLOCKS | XFS_SB_FEATURES2 | \
> +	 XFS_SB_BAD_FEATURES2)
>  
>  
>  /*
> @@ -297,6 +320,14 @@ static inline int xfs_sb_good_version(xf
>  }
>  #endif /* __KERNEL__ */
>  
> +/*
> + * Detect a bad features2 field
> + */
> +static inline int xfs_sb_has_bad_features2(xfs_sb_t *sbp)
> +{
> +	return (sbp->sb_bad_features2 != 0);
> +}
> +
>  #define	XFS_SB_VERSION_TONEW(v)	xfs_sb_version_tonew(v)
>  static inline unsigned xfs_sb_version_tonew(unsigned v)
>  {
> 
>